Method of making the same



Aprll 10, 1956 J. B. BRENNAN Re. 24,141

REINFORCED ACOUSTIC DIAPHRAGMS AND METHOD OF MAKING THE SAME Original Filed Oct. 25, 1952 FZ 'QJ X Z 6 3 a I IN VEN TOR.

I by m, 7 W swam ATTORNEYS.

United States Patent 1 24,141 REINFORCED ACOUSTIC DIAPHRAGMS AND METHOD OF MAKING THE SAME Joseph B. Brennan, Cleveland, Ohio No. 2,716,462, dated August 30, 1955, Serial 0. 316,874, October 25, 1952. Application for reissue November 7, 1955, Serial No. 545,585 10 Claims. (Cl. 181-32) Matter enclosed in heavy brackets II] appears in the original patent but forms no part of this reissue specification; matter printed in italics indicates the additions made by reissue.

This invention relates to reinforced acoustic diaphragms and method of making the same, and more particularly to the manufacture of flexible concave diaphragms of the type used in loud speakers.

In my copending application Serial Number 729,846, filed February 20, 1947, now Patent No. 2,624,417, issued January 6, 1953, there is disclosed and claimed a diaphragm formed of a felted fibrous sheet whose rim and body portions are reinforced by radially extending strands which are embedded in and bonded to the felted fibrous material. Reinforcing of the body improves the air displacement characteristics thereof to increase the efiiciency of the diaphragm and to control the resonance characteristics. Reinforcing of the rim portion provides the necessary radial strength without sacrifice of lateral flexibility so that resonance can be controlled as desired and edge break-up avoided.

It is one of the objects of the present invention to provide a reinforced acoustic diaphragm and method of making the same in which the diaphragm is reinforced by a plurality of circumferentially spaced filaments of plastic material extending radially across the diaphragm body portion and rim and adhering to the felted fibrous material of which the diaphragm is formed.

According to one feature of the invention the filaments of plastic material may be pressed into the felted sheet to be embedded in the surface thereof.

Another object is to provide a method according to which plastic material is deposited on the sheet of felted fibrous material of which the diaphragm is formed in a plurality of circumferentially spaced filaments and is then set.

The plastic material may be thermoplastic applied in heated condition and cooled to set it or may be softened by a solvent and set by evaporating the solvent.

According to another feature of the invention the felted diaphragm sheet may be masked to control application of the plastic thereto quickly and easily.

The above and other objects and features of the invention will be more readily apparent from the following description when read in connection with the accompanying drawing in which:

Figure l is an elevation of a diaphragm embodying the invention.

Figure 2 is an enlarged partial cross section.

Figure 3 is a view similar to Figure 2 showing an alternative construction; and

Figures 4 and 5 are views similar to Figure 2, illustrating the steps in alternative methods of making the diaphragms.

The diaphragm as shown in Figure 1 may comprise a sheet of felted fibrous material formed with a concave body portion 10, which is preferably conical and which terminates at its apex in a cylinder cup-shaped extension 11 to carry a speaker coil. The body of the diaphragm terminates at its periphery in a laterally extending annular rim 12, which may be corrugated as in conventional diaphragm constructions to increase its flexibility.

According to the present invention the diaphragm is reinforced by a plurality of radially extending filaments 13 formed of plastic material. The filaments extend 'across the rim 12 and cross all or a part of the body 10 as desired to provide the desired degree of stiffness in the body portion, and the desired degree of strength and stiffness in the rim portion. Certain of the filaments may be relatively short, as shown, to extend only partially across the body while others may extend diametrically completely across the diaphragm. The filaments in the body portion stiffen and reinforce the concave body to improve its air displacement characteristics and to control the resonance of the diaphragm. The filaments extending across the rim portion impart thereto the necessary radial strength to support the diaphragm properly while providing the necessary flexibility to permit the body portion of the diaphragm to vibrate in the desired manner:

sheet to its completed form in which it is compressed,

and dried and then depositing the plastic filaments thereon and setting them. It is contemplated that the plastic filaments may be formed of a thermoplastic resinous material applied in heated condition to the diaphragm sheet and then cooled to set it. Alternatively, a resinous plastic material may be employed which is softened by the addition of the solvent so that it can be applied to the diaphragm sheet and which is then set by evaporating the solvent.

Instead of the filments being disposed on the surface of the sheet, as indicated in Figure 2, they may be embedded therein as illustrated in Figure 3. As shown in this figure, the diaphragm sheet 10' has the plastic filaments 13' pressed into its surface to lie substantially .fiush therewith. This construction may be made by closely against one surface of the diaphragm sheet illus trated at 10. Thesheet 14 may be formed with a series of relatively narrow slots 15 therein which can be filled with plastic material to form the filaments.

Figure 4 illustrates a process of applying a thermoplastic material in heated condition or a resinous plastic softened to putty consistency by a solvent. As shown, such materail may be deposited over the mask 14 and excess material scraped from the mask by a doctor blade 16 to leave the slots 15 filled flush with the surface of the mask. Thereafter the mask may be removed and the plastic material set and the diaphragm will be completed.

Instead of the process described above the slots 15 may be filled as shown in Figure 5 by spraying plastic material into them from one or more spray nozzles 17. When spray nozzles are used it may be possible in many cases to omit the mask and deposit narrow strips of plastic material directly from the nozzles onto the blank. Either a thermoplastic resin is used which is heated sufiiciently to make it soft enough to spray or a solvent may be added to the plastic resin to soften it sufficiently for spraying. A sufiicient quantity of plastic material is sprayed in either case to fill the slots 15, and after drying or at least partial setting of the plastic material, the mask can be removed. a

fiedfh'phra'g'mma'y be formed in the usual manner by depositing the fibrous-material andrompre'ssing' it in a' mold before the reinforcing" filaments are applied, this methodbeing preferred when the-filaments are on the surface 'o'f the diaphragm as shown in Figure When: the "filaments are to be embeddedas shown in Figure 3 they are deposited on the soft fibrous blank which is then pressed in a mold to complete the diaphragm and force the filaments into its surface. I M The completed diaphragm provides a concave body portion adequately reinforced to provide the necessary degree of stiflness and strength and a rim portion having the requisite radial strength to support the diaphragm and fat the same time with the necessary flexibility for proper operation. The diaphragm car! be manufactured easily andinexpensively in the manner described above.

by controlling the areas or patterns on the diaphragm on which the plastic material is deposited, it' is possible to vary the resonance accurately over a wide range. Thus, in addition to the filaments or strips extending. radially across the rim it may be desirable to coat the central portion or all of the concave body portion or to form annular strips of filaments on the body portion. As examples ofthese types of coating the diaphragm of Figure l is shown as formed with an annular strip or filament 18 of plastic material and with coated areas 19 between the strip 18 and the rim to stiffen the concave body portion.

While the invention has been disclosed in connection with one particular type of diaphragm it will be understood that this disclosure is for the purpose of illustration only and is not to be taken as a definition of the scope of the invention, reference being had for that purpose to the appended claims.

What is claimed is: v i

vl. An acoustic diaphragm having a concave body portion and a peripheral mounting rim extending laterally of the body portion, said body and rim portions be ing integrally formed of vfeltedfib rous material in a relatively thin flexible continuous sheet, and a plurality of separate filaments extending radially across at least a part of the rim and body portions and circumferentially spaced from each other, each of said filaments being formed by a strip of resinous plastic material adhesively secured to the fibrous sheet. k

2. An acoustic-diaphragm having a concave body portion and a peripheral mounting rim extending laterally of the body portion, said body and rim portions beingv integrally formed of felted fibrous material a rela: tively thin flexible continuous sheet, and a plurality of separate filaments extending radially across at least a part of the rim and body portions and circumferentially spaced from each other, each of said filaments being formed by a strip of resinous plastic material adhesively secured to the fibrous sheet and projecting above the surface of the sheet.

3. An acoustic diaphragmhaving a concave body portion and a peripheral mounting rim extending laterally oi the body portion, saidbody andrim portions being integrally formed of felted fibrous material in a rela# tively thin flexible continuous sheet, and a plurality of separate filaments" extending radially across at" least a part of the rim and body portions and 'circurnferent'ially spaced from each" other, eachof said filaments" being fanned by a strip of resinous plastic'material adhesiveiy secured to the fibrous sheet and embeddedin the sheet so that its outer surface lies substantially flush with the surface of the sheet.

4. The method of making 'acousticdiaphragms' vs hich comprises forming a continuous felted fibrous sheet into a diaphragm with a concave body portion and a peripheral mounting.rim-extending laterally ofbody portion, depositing resinous material on the sheet in the form: of a plurality of spaced filaments extending radially eral mounting rim extending 4 across at least a part of the rim and body portions of thediaphragm, andsettingnhe "resinous material:

5. The method of making acoustic diaphragms which comprises forming a continuous felted fibrous sheet into a diaphragm with-a concave body portionand aperipheral mounting rim extending laterally" o'f the body portion, depositing resinous material ,onthe sheet in theform of a plurality of spaced filaments exten ding. radially across at least party the rim and pur pressing the filamentsinto the the surface thereof, and settially' spaced filaments extending radially across at leizst a part of the body [portion] and rim portions", and

cooling the thermoplastic material to set it.

7. The method of making acoustic dia hragm which:

comprises forming a continuous felted fibrous sheet into a diaphragm with a concave body portion and a' periphlaterally of the body portion, depositing heated thermoplastic resinous material on the sheet in the form of a plurality of circumferentially spaced filaments extending radiallyacrossat' least a part of the body [portion] and rim' portions, press ing the filaments into the sheet to embed them in thje su'rfacethereof and simultaneously to compress the sheet;

and cooling the thermoplastic material to set it. v

8. The method of making acoustic diaphragms' which comprises forming a continuousfeltedj fibrous" sheet into a diaphragm with a concave body portion and a peripheral mounting rim extending laterally of the body portion, depositing'on the sheet a resinous plastic material softenedby a volatile solvent in the form of a plurality of circumferentially spaced filaments extending radially across at least a part of the body [portion] and rim portions, and evaporating the solvent from the resinous material to set it. p I

9. The method of making acoustic diaphra'grns which comprises forming a continuous'felted fibrousshe'et into a diaphragm with a concave body portion and a periph eral mounting rim exteridin'g'latera'lly of the body portion, masking one surface of the sheet to leave exposed only aplurality of circumferentially spaced narrow strips extending radially across at lea'st' aj part of the body [portionIand rim portions, covering'the exposed stripswith resinous plastic material to form plastic filaments extending radially across the body portion and rim, and

V removing the masking.

of making acoustic diaphragms which comprises forming a continuous felted fibrous sheet into a diaphragm with a concave body portion and a peripheral mounting rim extending laterally of the body portion, covering one surface ofthe sheet with a relatively thin mask formed with a plurality of circumfcrentially spaced narrow slots therein extending radially across at least a part of the body'[portiori] and rim portions-filling the slots with resinous plastic material to form on the sheet a plurality of filaments extendingradially across the body portion and rim, and removing the mask 10. The method from the sheet.

Refrences-Cited in the fileofthis patent or the original patent UNITED STATES PATENTS 246,552 Cookson Nov. 13, 1917 1,742,398 Kelley Jan. 7, 19-39 1,745,405 Clement Feb=- 4; 1930 1,997,790- Heidrich Apr. 16, 19-35 2,037,666 Pennington Apr. 14, 1936 2,284,480 Rohweder et al, Sept. l i942 

